IP2 And IP3 Accurate and Rapid Measurement.pdf

The Designer’s Guide Community downloaded from Accurate and Rapid Measurement of IP2 and IP3 Ken Kundert Designer’s Guide Consulting, Inc.Version 1b, 22 May 2002 Describes a new approach to computing IP2 and IP3 with SpectreRF that is both faster and more accurate than the traditional approach. Also given is a way of rapidly estimat- ing CP1dB. Last updated on March 10, 2009. You can find the most recent version at www.designers- . Contact the author via e-mail at ken@. Permission to make copies, either paper or electronic, of this work for personal or classroom use is granted without fee provided that the copies are not made or distributed for profit or commer- cial advantage and that the copies are complete and unmodified. To distribute otherwise, to pub- lish, to post on servers, or to distribute to lists, requires prior written permission.Copyright ? 2009, Kenneth S. Kundert – All Rights Reserved 1 of 13 Intermodulation Distortion1.0 Intermodulation Distortion At low frequencies, it is common to quantify the nonlinearity of a circuit by indicating the distortion in the output signal when driven by a sinusoid that achieves a certain out- put level. At high frequencies, and particularly with narrowband circuits, it is more common to characterize the distortion produced by a circuit in terms of a compression point or an intercept point. These metrics characterize the circuit rather than the signal, and as such it is not necessary to specify the signal level at which the circuit was charac- terized. 2.0 Compression Points To measure the compression point of a circuit, apply a sinusoid to its input and plot the output power of the fundamental as a function of the power of the input. The 1 dB com- pression point is the point where the gain of the circuit has dropped 1 dB from it small- signal asymptotic value. This is illustrated in Figure 1. iCP1dB is the input power and oCP1dB is the output power that corresponds to the 1 dB compression point. iCP is nor-